The present invention relates to a method for preparing an adjusted milk whey protein maintaining a state of transparent solution or gel, and to a method for preparing an adjusted milk whey protein product which can stably maintain water retention, viscosity, emulsifiability and foaming property good against heating and cooling in a low protein concentration even under salt-containing condition.
Milk whey is the name of a fraction prepared by removing fat and casein from milk and its main protein components are .beta.-lactoglobulin, .alpha.-lactalbumin and whey albumin. Such milk whey and milk whey protein are available as the secondary products of dairy product processing in large amount and economically and excellent in taste. Accordingly, they have been recently widely accepted in the foodstuff market as milk whey drinks and milk whey powders.
Furthermore, since milk whey protein has functions of gel formation, foaming, emulsification and the like, it can be used as the raw material for foodstuff processing. However, its application is limited to the gelling agent for foodstuff and the nutrition aid and now it is substantially not used in the industries other than foodstuff industry. The reason is the milk whey protein products manufactured hitherto had unsatisfactory gelling property, viscosity, emulsifiability and foaming property. Especially, it is difficult to prepare its transparent solution and gel.
Polysaccharides or gums such as agar, alginic acid, pectin and carrageenan, animal proteins such as gelatin and vegetable proteins such as glycinin and gluten and various synthetic polymers have been mainly used as the thickening and gelling agents in the commercial products such as foodstuffs, pharmaceuticals and cosmetics. However, they are not economical and insufficient in function and nutrition, and further cannot keep sufficient viscosity and gelling property at an elevated temperature of not lower than 100.degree. C. and under a refrigerated condition of not higher than 0.degree. C. to be lowered in viscosity and to cause water separation and to lose gelling property. Hence, they can exert their effect only in the ambient temperature region. In the presence of a salt, they tend to form an opaque gel or sol and cannot be used for an application requiring transparency.
Further, transparent gel bases include alkali-treated egg white, protease-treated food proteins. However, alkali treatment causes lowering of nutritive value of protein. Enzyme treatment requires expensive enzyme in a large amount and accordingly is not economical. Thus, they have several problems.
In these methods, in all cases, when heated in the presence of a salt, turbid gel or turbid solution is formed and the turbid solution is low in viscosity and its use as a thickener is limited and is also low in emulsifying power and foaming power. Turbid gel is also low in water retention and elasticity to cause several problems.
An object of the present invention is to provide a product which can maintain transparency stably with no lowering of nutritive value by heating from milk whey protein excellent in economics and functions as mentioned above.
An another object of the present invention is to provide a method for the preparation of a new adjusted milk whey protein which forms a viscous transparent or turbid solution or a transparent gel under a salt-containing condition or under low protein concentration.
Further, an another object of the present invention is to provide a simple and economical method for a milk whey protein product which can stably maintain the functions including viscosity, gel property, emulsifiability and foaming property even at an elevated temperature not lower than 100.degree. C. and under a refrigerated condition of not higher than 0.degree. C. and is rich in functionality.